1. Field of the Invention
This invention generally relates to small-sized step motors that are capable of generating enough detent torques, and more particularly, to a drive mechanism in a camera that employs the-aforementioned step motor.
2. Description of the Related Art
In recent years, cameras have become electronics devices and shutters thereof are driven by the step motors. In this type of cameras, it is desirable to include a mechanism in which the battery consumption can be suppressed and a shutter blade or diaphragm blade can be retained even when the current does not flow. Therefore, Japanese Patent Application Publication No. 2001-61268 (hereinafter, referred to as Patent Document 1), for example, proposes a step motor having a magnetic member that applies a lock force so that a rotor comes to a given position without swinging when the current does not flow through a coil. With such step motor, it is possible to stop the rotor at an accurate position at the time of stopping the motor and suppress the power consumption. In addition, Japanese Patent Application Publication No. 2003-21857 (hereinafter, referred to as Patent Document 2) discloses an invention relating to a shutter for a digital camera and proposes a shutter mechanism, thereby the shutter can be left open or closed even while the current is not flowing and the power consumption is suppressed.
The step motor disclosed in the afore-mentioned Patent Document 1 additionally includes the magnetic member to apply the lock force to the rotor. In addition, the motor used for the shutter disclosed in the afore-mentioned Patent Document 2 is formed in such a manner that magnetic poles of the stator facing an outer circumferential surface of the magnet are formed to have a complicated comb-like shape. Hence, the motors described in the above-mentioned conventional technique additionally include a member or needs a complicated processing, resulting in problems such as a complex motor structure and increased manufacturing costs.